Swivel hitch with improved mounting of lower gearbox

ABSTRACT

A primary drive line for delivering power from a power-take-off (pto) shaft on a tractor to an input shaft on an implement includes a swivel hitch comprised of an upper gearbox and a lower gearbox. The upper gearbox is fastened to a pair of spaced apart, upper vertical plates carried on a tongue extending forwardly from the implement, and the lower gearbox is fastened to a pair of spaced apart, lower vertical plates carried by a yoke assembly that is attached to the tractor. An output shaft on the upper gearbox is coupled to the implement input shaft. The lower gearbox has two shafts, the first of which is coupled to an input shaft on the upper gearbox. The second shaft on the lower gearbox is connected to the tractor pto shaft. The lower gearbox is mounted by using bushings with rubber inserts which permit limited repositioning of the lower gearbox with respect to the yoke assembly in order to compensate for any misalignment of the lower gearbox first shaft when coupling it to the upper gearbox input shaft.

BACKGROUND OF THE INVENTION

This invention relates generally to agricultural machines and, inparticular, to a swivel hitch for connecting an implement to a tractor.

U.S. Pat. No. 4,738,461 to Stephenson et al discloses a swivel hitchincluding an upper gearbox coupled to an input shaft on an implement anda lower gearbox connected to a power-take-off shaft on a tractor. Inorder to achieve the desired maneuverability of the implement duringnormal operation, the lower gearbox rotates relative to the uppergearbox about a vertical axis when the tractor makes turns. The uppergearbox is rigidly mounted on a tongue extending forwardly from theimplement and has an input shaft coupled to an output shaft on the lowergearbox by a coupling device. The lower gearbox is rigidly bolted to abracket carried by a hitch adaptor that is attached to the tractor. Ifthere is any misalignment between the lower gearbox output shaft and theupper gearbox input shaft, it will be difficult to couple these shaftstogether.

SUMMARY OF THE INVENTION

The present invention is directed to an arrangement wherein apower-take-off shaft on a tractor delivers power through a primary driveline to an input shaft on an implement. The primary drive line includesa swivel hitch comprising an upper gearbox fastened to a tongueextending forwardly from the implement, and a lower gearbox mounted on ayoke assembly that is attached to the tractor. The upper gearbox has aninput shaft and an output shaft with the upper gearbox output shaftbeing coupled to the implement input shaft. The lower gearbox has firstand second shafts with the first shaft being coupled to the uppergearbox input shaft and the second shaft being connected to the tractorpower-take-off shaft. The lower gearbox is mounted by means permittinglimited repositioning of the lower gearbox with respect to the yokeassembly in order to compensate for any misalignment of the lowergearbox first shaft when coupling it to the upper gearbox input shaft.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a tractor connected to an implement inaccordance with the present invention;

FIG. 2 is an enlarged sectional view taken along lines 2--2 in FIG. 1;

FIG. 3 is a sectional view taken along lines 3--3 in FIG. 2; and

FIG. 4 is an enlarged sectional view taken along lines 4--4 in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a tractor 10 is connected to an implement 12such as a mower-conditioner. The tractor 10 has a pair of rear wheels14, and the implement 12 has a pair of wheels 16. A power-take-off (pto)shaft 18 on the tractor 10 delivers power to an input shaft 20 on theimplement 12 through a primary drive line which includes a swivel hitch22 and a telescoping drive shaft 24 with conventional U-joints 26 ateach end thereof. The pto shaft 18 is connected to an end coupler 24a onthe drive shaft 24.

A tongue 28 has its trailing end 30 pivotally connected to the implement12, and a hydraulic cylinder 32 is connected between a bracket 33 on thetongue 28 and another bracket 34 on the implement 12. The leading end 36of the tongue 28 carries a pair of spaced apart, upper vertical plates38 between which is fastened by six bolts 40 an upper gearbox 42containing bevel gears 42a, 42b. Upper gearbox 42 has an output shaft 44rigidly coupled to the implement input shaft 20 by a coupling sleeve 46.An input shaft 48 of the upper gearbox 42 is rigidly coupled by anothercoupling sleeve 50 to a first shaft 52 on a lower gearbox 54 containingbevel gears 54a, 54b. Lower gearbox 54 is fastened by four bolts 56 to apair of spaced apart, lower vertical plates 58 that are carried by ayoke assembly 60. A second shaft 62 on the lower gearbox 54 is connectedto an end coupler 24b on the drive shaft 24. The tractor 10 has a threepoint hitch with an upper link (not shown) and a pair of lower links 64pivotally connected by pins 66 to the yoke assembly 60.

The bolts 56 extend through bushings 68 as seen in FIGS. 3 and 4. Ahorizontal plate 70 is fixed to the upper vertical plates 38, and apivot tube 72 is welded to the plate 70. Surrounding the pivot tube 72is a pivot housing 74 which is fastened by bolts 76 to the lowervertical plates 58. Referring to FIG. 4, the bushings 68 each include anouter sleeve 78 formed of a suitable metal such as steel that is weldedto one of the lower vertical plates 58, and a rubber insert 80 disposedinside the outer sleeve 78. The rubber insert 80 is bonded to an innersleeve 82 which is also formed of a suitable metal such as steel. Thebolts 56 have washers 57 associated therewith and they extend throughthe bushings 68 into threaded engagement with the lower gearbox 54 sothat a small clearance C is provided between each of the plates 58 andthe lower gearbox 54. These clearances C and the rubber inserts 80 inthe bushings 68 cooperate to permit limited repositioning of the lowergearbox 54 in order to compensate for any misalignment of the lowergearbox shaft 52 when it is being coupled to the upper gearbox inputshaft 48 by the coupling sleeve 50.

The hydraulic cylinder 32 may be extended or retracted to swing theimplement 12 between a normal operating position shown in FIG. 1 wherethe implement 12 is disposed outboard of the tractor 10 and a transportposition (not shown) where the implement 12 is disposed generally behindthe tractor 10. When the implement 12 is swung between its normaloperating position and its transport position, the tongue 20 is pivotedat its leading and trailing ends 36, 30 thereby resulting in the uppergearbox 42 being pivoted about a generally vertical axis Y relative tothe lower gearbox 54.

During normal harvesting operation of the tractor 10 and the implement12, the tractor 10 makes right and left turns in order to maneuver theimplement 12. When the tractor 10 turns, the lower gearbox 54 rotateswith respect to the upper gearbox 42 about the vertical axis Y. Thepivot housing 74 rotates on the pivot tube 72, but the gearboxes 42, 54are not used as structural members. The draft load applied to thetractor 10 by the implement 12 does not pass through the gearboxes 42,54 but is transmitted through tongue 28, upper vertical plates 38,horizontal plate 70, pivot tube 72, pivot housing 74, lower verticalplates 58, yoke assembly 60 and lower links 64.

The gear ratios of the gearboxes 42, 54 are identical and they areselected to accommodate either a tractor with a 540 rpm pto shaft or atractor with a 1000 rpm pto shaft while maintaining the same speed forthe implement input shaft 20. When changing tractor pto speeds (e.g.from 540 rpm to 1000 rpm), the lower gearbox 54 is unfastened from thelower vertical plates 58, rotated about a diagonal axis A, and thenrefastened to the lower vertical plates 58 so that its shaft 62 iscoupled to the input shaft 48 of the upper gearbox 42 while its shaft 52is connected to the drive shaft 24. The coupling sleeve 50 connectingthe respective shafts 48, 62 of the gearboxes 42, 54 is changed toaccommodate the differences in splines on the shafts 52, 62. The driveshaft 24 is also disconnected and rearranged end for end to accommodatethe differences in splines between a 540 rpm tractor pto shaft and a1000 rpm tractor pto shaft. In other words, the drive shaft end coupler24b is connected to the pto shaft 18, and the drive shaft end coupler24a is connected to the lower gearbox shaft 52.

It will be understood that on a 540 rpm tractor, the pto shaft 18 hassix straight splines, whereas on a 1000 rpm tractor, the pto shaft 18has twenty-one involute splines. The end coupler 24a on the drive shaft24 has six straight grooves for mating with the six straight splines onthe 540 rpm tractor pto shaft. The other end coupler 24b on the driveshaft 24 has twenty-one involute grooves for mating with the twenty-oneinvolute splines on a 1000 rpm tractor pto shaft. The shaft 62 on thelower gearbox 54 has twenty-one involute splines that mate with the endcoupler 24b on the drive shaft 24, and the shaft 52 on the lower gearbox54 has six straight splines that mate with the end coupler 24a of thedrive shaft 24. The input shaft 48 on the upper gearbox 42 hastwenty-one involute splines while the output shaft 44 on the uppergearbox 42 has six straight splines. The implement input shaft 20 hastwenty-one involute splines. The coupling sleeve 46 has six straightgrooves on one end to mate with the six straight splines on the uppergearbox output shaft 44, and twenty-one involute grooves on the otherend to mate with the twenty-one involute splines on the implement shaft20. When a 540 rpm tractor is used, the coupling sleeve 50 hastwenty-one involute grooves on one end to mate with the twenty-oneinvolute splines on the upper gearbox input shaft 48, and six straightgrooves on the other end to mate with the six straight splines on theinput/output shaft 52 of the lower gearbox 54. When using a 1000 rpmtractor, the coupling sleeve 50 has twenty-one involute grooves on eachend to mate with the twenty-one involute splines on both the uppergearbox input shaft 48 and the lower gearbox shaft 62.

What is claimed is:
 1. In an arrangement wherein a power-take-off shafton a tractor delivers power through a primary drive line to an inputshaft on an implement, said primary drive line including a swivel hitchcomprising:an upper gearbox fastened to a tongue extending forwardlyfrom the implement, the upper gearbox having an input shaft and anoutput shaft with said upper gearbox output shaft being coupled to saidimplement input shaft; a lower gearbox mounted on a yoke assembly thatis attached to the tractor, the lower gearbox having first and secondshafts with said first shaft being coupled to said upper gearbox inputshaft and said second shaft being connected to said tractorpower-take-off shaft said yoke including a pair of spaced apart, lowervertical plates; and said lower gearbox being mounted by resilient meanspermitting limited repositioning of said lower gearbox with respect tosaid yoke assembly in order to compensate for any misalignment of saidfirst shaft when coupling it to said upper gearbox input shaft, saidresilient means including a plurality of bolts which extend throughcorresponding bushings having rubber inserts, each said bolt passingthrough a corresponding sleeve fixed to an adjacent one of said lowervertical plates and being threadably received in said lower gearbox,said rubber inserts being disposed between the corresponding said sleeveand bolt and being compressed between a washer and said lower gearbox.2. The arrangement of claim 1, wherein said first shaft on said lowergearbox is rigidly coupled to said input shaft on said upper gearbox bya coupling sleeve.
 3. The arrangement of claim 2, wherein said lowergearbox first shaft and said upper gearbox input shaft have splineswhich mate with grooves in opposite ends of said coupling sleeve.
 4. Thearrangement of claim 1, wherein said bushings are arranged so thatclearances are provided between said lower vertical plates and saidlower gearbox to assist in permitting said limited repositioning of saidlower gearbox.